The present invention relates to an optical reader for a high-resolution optical coder used in particular to determine the angular position of one object relative to another.
Optical coders are known from the prior art which allow measuring the angular position of two objects that may be in relative motion by means of interferometry. Such a device is known from the European patent applications 262,349 and 419,701 in the form of a disk fitted along a peripheral annulus with angular graduations allowing to diffract in a first instance a light beam from a light source. Once diffracted, the light beam enters a prism deflecting it to a read-unit diametrically opposite the light source. Before reaching the read unit, the light beam again crosses the disk and is diffracted a second time by the angular graduation. The beam is also totally reflected on the prism's side faces, thereby producing interferences.
An optic pickup is further known from the French patent 2,666,145 and in particular acts as a speed detector or a position detector of a rotating or translating element. This pickup comprises a coding element fitted with reflecting surfaces of defined geometry and a transducer comprising an optical emitter and an optical detector. The speed of the coding element is sensed on account of the light-beam reflections on the particular surfaces of the coding element. These surfaces are bounded at least in part by a conical surface, that is a parabola, an ellipse or a hyperbola. Because of the manufacture of the coding element, this pickup requires high-accuracy machining ands thus entails large costs and high fragility.